Device for detecting rotation



O United States Patent m13,551,691

[721 inventors Katsutoshi Nishimura; [56] References Cited KiyojiFujisawa; Isao Kozu; Kozo UNITED STATES PATENTS 2,927,474 3/1960 Peras317/5x P 771,905 968 2.929023 3/1960 Mischon etaL. 34o/271ux [221 PM3,062,988 11/1962 Fitch etal........ 340/271ux [45] Patented Dec. 29,1970 3,120,655 2/l964 Beason etal..... 340/271 [731 g z fi g lzg3,276,256 10/1966 Rudasill m1. 340/271x 32 priority No 2: 19 7 PrimaryExaminer-Robert K. Schaefer 33 Japan Assistant Examiner-T. B. Joike [342 710 19 Attorney-Wenderoth, Link & Ponack ABSTRACT: A rotationdetecting device. A mechanical [54] F Q ROTATION switch is providedwhich operates as a single-pole double throw switch. An electric circuitis responsive to the action of [52] U.S.Cl 307/120, the mechanicalswitch. The mechanical switch comprises a 340/27]; 3 l7/5 rotating bodywhich has at least one conductive segment on [Sl] lnt.Cl ..H01h /02 thesurface thereof and contacts for electrically connecting Field of Search307/] I6, the rotating body with the electric circuit. The electriccircuit 119, I22, I20; 340/27lX; ZOO/61117; 3 l7/5X; includescapacitors, the electric charge of which is controlled 324/CG by therotation of the rotating body.

- PATENTEDnaczsmm 8551, 691 SHEET 1 BF 3 INVENTORS KATSUTOSHI NlSl-HMURAKIYOJ] FUJISAWA ISAO KOZU KOZO YAMAMQTO ATTORNEYS PATE'NTEDBEmIQm3,551,691

SHEET 3 BF 3 KATSUTOSHI NI U KIYOJI FUJI R ISA ZU KOZU YAMAMOTO A NEYing any mechanical load thereon, and a controlling means which isresponsive to the mechanical switch.

A conventional rotation detecting device comprises a switch having threecontact segments, the middle one of which is an armature and is longerthan the other two. An eccentric cam rigidly secured to a rotating shafthits the longest contact segment of the conventional switch duringrotation of said shaft. Upon being hit by said eccentric cam, the switchis placed in an opened circuit or in a closed circuit position. Such aswitch imposes an undesired mechanical load on the shaft. It isdesirable that. the mechanical load be as low as possible. Theundesirable mechanical load can be lowered by using a switch which isoperated by an extremely low force. However, such :rswitch is not easyto manufacture and is expensive in addition to having inferiordurability.

Therefore, one object of the present invention is to provide a rotationdetecting device which is capable of controlling another device which isto be operated in accordance with the rotation of a rotating bodywithout imposing any mechanical loa'don the rotating body.

Another object of the present invention is to provide arotationdetecting device capable of measuring the speed of rotation of arotating body without imposing any mechanical load on the rotating body.

A further object of the present invention is to provide a rotationdetecting device including a mechanical switch which comprises arotating shaft which can be a reel spindle of a tape recorder.

The rotation detecting device according to the present inventioncomprises a mechanical switch and a controlling means responsive to saidmechanical switch. Said mechanical switch comprises a rotating bodywhich is made up of a shaft and a rotor having at least one conductivesegment on the surface thereof and electric contacts coupledelectrically with said rotating body. The conductive segments on therotating body and said electric contacts are arranged to act as asinglepole double throw switch.

The invention will be more fully described in the followingspecification taken together with the accompanying drawings,

wherein:

FIG. 1 is a perspective view of a mechanical switch according to thepresent invention;

FIG. 2 is a crosssectional view of the mechanical switch according tothe invention;

- FIGS; 3 to 6 are schematic plan views of the switch indifferenvoperatingpusitions;

FIG. 7 is a circuit diagram of a rotation detecting device combined witha mechanical switch and controlling circuit in accordance with thepresent invention;

FIG. 8 is a cross-sectional view of another embodiment of a mechanicalswitch-according to the invention;

I'FIGSL 9-1 I are perspective views of other embodiments of themechanical switch according to the present invention; and

--FIG. 12 is acimuit diagram of a rotation detecting device liaving aspan thereof the mechanical switch of FIG. 1, and beingcombined withanother controlling circuit.

rFlOJI shows-arrembodiment of a mechanical switch contnnplatedby'thopresent invention. In FIG. I, a rotating body 8 is comprised of ashaft 1 and a rotor 2 rigidly secured to said shaft 1. The rotating body8 is rotatably supported on a frame 9. Said rotor 2 is made of anonconductive material such as organic resin or ceramic material and hastwo conductive segments 3 and 4 set into the peripheral surface thereof.Three electric contacts 5,6 and 7 have their one ends fixed to saidfrar'rie9 and theother ends are in contact with the periphery of saidrotor 2 so asto contact said conductive segments 3 and 4 intermittently,inaccordance with the rotation of said rotor 2.

Said electrical contacts are designated the first electric contact 5,the second electric contact 6 and the third electric contact 7, andarepreferably electrical brushes having a resilient arm which ensures agood electrical contact with said conductive segment 3 or 4. Saidconductive segments 3 and 4 are set into the surface of said rotor 2 soas to form a substantially smooth surface therewith.

In the position of the device as shown in FIG. 2, said rotating body 8is in contact with the first, second and third electric contacts 5, 6and 7 at contacting points 5', 6 and 7', respec tively. Said firstelectric contact 5 is electrically connected, through said segment 4,with said third electric contact 7, while said second contact 6 iselectrically isolated from said first and third electric contacts 5 and7. At the position shown in FIG. 3, contact 5 is electrically isolatedfrom both contacts 6 and 7. At the position as shown in FIG. 4, thefirst contact 5 is electrically connected, through said segment 3, withsaid second contact 6 while said third contact 7 is electricallyisolated from said first and second electric contacts 5 and 6. It isimportant that said first electric contact 5 can be electricallyconnected, through one of said segments 3 and 4, with either one of saidsecond and third electric contacts 6 and 7,-but that said third electriccontact 7 is never electrically connected with said second electriccontact 6 during the rotation of said rotating body 8.

This can be accomplished by making the length of the arc betweencontacting points 5 and 6' substantially equal to that betweencontacting points 5 and 7' and shorter than the arc length of segments 3and 4, and by making the arc length of segments 3 and 4 substantiallyequal to each other and the arc length between contacting points 6 and7' longer than that of segments 3 or 4.

With such an arrangement of electric contacts 5, 6 and 7, and segments 3and 4, the electrical connections between said first electric contact 5and said second electric contact 6 and between said first electriccontact 5 and said third electric contact 7 are alternatively in aclosed circuit and an open circuit during the rotation of said rotatingbody 8. Therefore, the mechanical switch according to the presentinvention acts as a single-pole double throw switch. During the rotationof the rotating body 8, the relationship of said contacting points andconductive segments are changed in turn, as shown in FIGS. 2- -6.

In the circuit of FIG. 7, said first electric contact 5 is connected toa power supply 16 through a resistor 10 and a capacitor 11. Said secondelectric contact 6 is connected to a junction point 17 of two electricalcircuits, one of which extends to said power supply 16 through acapacitor 12, and the other of which extends to the base of a transistor14 through a resistor 13. Said third electric contact 7 is directlyconnected to said power supply 16. Said transistor 14 has a groundedemitter and has the collector connected to said power supply 16 througha solenoid coil 15.

When said mechanical switch is in the switching position as shown inFIG. 7, the first electric contact 5 is connected to the third electriccontact 7 through the conductive segment 4. In this circuit condition,the voltage across the capacitor 11 is equal to zero because thecapacitor 11 is short-circuited by the resistor 10 which protects theelectric contacts 5 and 7 and the conductive segments 3 and 4 fromaccidental damage due to an extremely high discharge current from thecapacitor 11. On the other hand, the voltage V across the capacitor 12is substantially equal to that of the power supply 16 because thecapacitor 12 is charged up to the voltage of power supply 16. Thevoltage V across the junction point 17 and ground becomes substantiallyequal to zero Accordingly, the transistor 14 is in a nonconductive statebecause there is no current flowing into the base of transistor 14.

When the mechanical switch is rotated to the switching position as shownin FIG. 4, the first electric contact 5 is connected to the secondelectric contact 6 through the conductive segment 3 and the capacitor 11is connected in parallel with the capacitor 12.

The voltage V across the capacitor 12 now drops abruptly toapproximately V .C /(C +C because the electric charge which waspreviously stored in the capacitor 12 is delivered to the capacitor 11.

As a result, the voltage V11 at the point 17 rises abruptly from toapproximately V"; /C,, 1(C +C 2), and a current of about V [R begins toflow into the base of transistor 14, and the transistor 14 becomesconductive. This allows a large current, i.e. sufficient to saturate thecoil 15, to flow from the power supply 16 to the collector of transistor14, the coil 15 is energized by said large collector current, and aplunger which is used as an output device of the rotation detectingdevice is actuated.

Thereafter, the voltage V will fall exponentially toward zero with atime constant 1'=(C, +C, R and the current V" /R will also decrease. Asa result, the current V R becomes zero and the transistor 14 againbecomes nonconductive.

As is well known, the voltage across a capacitor in a circuit composedof a resistor and a capacitor is expressed as a function of time. Inorder to ensure that said transistor 14 is conductive even when saidshaft 1 rotates slowly, it is necessary that the product CR of theresistor and capacitor, i.e. the time constant, be as large as possible.In order to shorten the time cycle of a mechanical switch having aninvariable time constant, it is necessary to increase the rotating speedof said shaft 1 or to increase the number of conductive segments.

When the shaft 1 stops, the transistor 14 is nonconductive regardless ofthe position of said rotor 2. Since the capacitor 12 is charged up to avoltage V over a relatively long time, with the switch in the positionof FIGS. 7, 3, 5 and 6, no base current flows and the transistor 14becomes nonconductive. In the position of FIG. 4', the parallelconnection of the capacitor 11 and the capacitor 12 causes the chargingtime of capacitors to be prolonged. Accordingly, a the time necessaryfor transistor 14 to be converted from the conductive state to thenonconductive state is longer than the charging timeof the capacitor 12.

Since the solenoid coil 15 is energized by the collector current oftransistor 12, the movement of the plunger gives an indication ofwhether the shaft 1 is rotating or stopped. The plunger can be coupledwith another device which operates in accordance with the rotation of ashaft 1.

It is preferable that said second electric contact 6 and third electriccontact 7 be disposed to contact the surface of said rotor 2 at oppositeends of a diameter of said rotor 2. It is also 'desirable for easymanufacturing that said two segments are opposed to each other andsubstantially the same length. Howcluding only one conductive segmentcan also act as a mechanical switch, and a mechanical switch having morethan three conductive segments can also act as a satisfactory mechanicalswitch.

Referring to FIG. 8, wherein the same references designate elements thesame as those of FIGS. 1 and 2, four conductive segments 18, 19, and 21,having the same length, are positioned symmetrically on the periphery ofrotor 2. Three electric contacts 5, 6 and 7 make contact with thesurface of said rotor 2 at the one side of the periphery of said rotor2. The arc length between conducting points 5' and 6 or 5' and 7 is lessthan the length of said conductive segments. Such an arrangement makesit possible to shorten the cycling time for switching action, and has aneffect similar to the effect of increasing the speed of rotation of theshaft II. I

It is not necessary to use three electrical contacts in the form ofresilient electric brushes. Referring to FIG. 9, a first electriccontact 55 is rotatably connected to a shaft 51 which is made of anelectrically conductive material. A second electric contact 56 and thirdelectric contact 57 are in contact with the side surface of a rotor 52in such a way that said second contact 56 contacts the upper portion ofthe periphery of the rotor and said third contact 57 contacts the lowerportion thereof. An upper conductive segment 53 hasa portion 22 whichcovers the upper flat surface of said rotor 52 and has projections 53and 53' extending down over the upper portion of the peripheral surfaceof said rotor 52. A third projection is not shown in FIG. 9. A lowerconductive segment has a portion which covers the lower flat surface ofsaid ro torf 52 and has three projections, only projection 54f beingvisible: extending up over the lower portion of he peripheral of rotor52, and which are'out of alig ment with the prbjec tions on the upperconductive segment 53. Both the upper conductive segment 53 and. lowerconductive segment'SWar electrically connected with the shaft 51. Suchan arrangement makes it possible to connect electrically said firstelectric contact 55 with said second electricc'ontact 56 or said thirdelec tric contact 57 in accordance with the rotation of said shaft 51.There is no possibility of completing a'circuit between said secondelectric contact 6 and said third electric contact 57.

Therefore, such an arrangement of conductive segments and electricalcontacts is similar to that of FIG. 1.

Another embodiment of the switch is shown in FIG. 10$ A first electriccontact 65 is rotatably connected to a shaft61 made of an electricallyconductive material. A second electric contact 66 and a third electriccontact 67' are positioned on opposite sides of a rotor 62 to contactthe'peripheral surface of said rotor 62. Three conductive segr ne 1523,24 and 25 cover the surface of said rotor 62, extending-from the upperface across the peripheral surface to the face. The end of each of thethree segments 23, 24,and 25fi's in contact with said shaft 61. It isimportant that said was and third electric contacts 66 and 67 and saidthree conductive segments 23, 24 and 25 be arranged in such a way thatboththe electric contacts 66 and 67 are not in contact with s'aidconductive segmentsat the same time. When one electric contact, forexample, the second electric contact 66, is'in c htact with one of thethree segments, the third electric contact 67 is not in con tact withany of the three segments. By usirig" uch a construction, it is possibleto complete a circuit between the first elec tric contact 65 and secondelectric contact 66or thir'd elec tric contact 67, in accordance withthe rotation of saidrotor 1'2.

FIG. 11 shows still another embodiment of the switch'.A third electriccontact 77 is rotatably connected to a shaft "71 made of a conductivematerial. A first electric contact 75 and a second electric contact76are in contact with the upper and" lower portions, respectively, or theperipheral surface of a rotor 71. An upper conductive segment 73 in theform of a strip is connected with said shaft 71 and extends across thetop and down the upper portion of the peripheral surface of said rotor72 to the middle thereof. A lower conductive segment 74 in the form of astrip extends across the whole'of the peripheral surface of said rotor72. Said upper segment 73 does not contact said second electric contact76. Both electric segments 73 and 74 are on the peripheral surface ofsaid' rotor 72 are separated from each other a distance greater'than theperipheral length of the contacting area of said electric contacts 75and 76. Such an arrangement makes it possible to complete a circuitbetween the first electric contact 75 and the third electric contact 77,while vthe second contact 76 is electrically isolated from both electriccontacts 75 and 77. When said lower segment 74 is in contact with saidfirst elec tric contact 75 andsecond electric contact 76 at the sametime, the third'contact 77 is electrically isolated from both electriccontacts 75 and 76.

FIG. 12 shows the circuit for a detecting device combined with anothercircuit, and similar reference numbers designate components similar tothose of FIG. 7. The first electric con-, j tact 5 is connected to thebase of a first transistor 28 through a resistor 35, a capacitor 33 anda resistor 31. The third electric contact 7 is connected directly to thecollector of a second transistor 30. Said capacitor 33 is connected tothe collector" of said second transistor 30 through a second capacitor34. The second electric contact 6 is connected to a junctionpoint 38between said resistor 31 and said first capacitor 33. The

collector of said first transistor 28 is connected to the base of saidsecond transistor 30.

The collector of said first transistor 28 is connected to a power supply16 through a resistor 29. The emitter of said first transistor 28 isgrounded. The collector of the second transistor 30 is connected to saidpower supply 16 through the solenoid coil 15. The emitter of said secondtransistor 30 is grounded through a resistor 36. Said junction point 38is connected to the collector of the second transistor 30 through aswitch 32.

When said switch 32 is open, said capacitor 33 and said capacitor 34 areshort-circuited alternatelythrough a resistor 35 by the mechanicalswitch during rotation of said mechanical switch. Such alemative shortcircuiting is equivalent to the use of a battery having a voltage ofabout zero for both the capacitors 33 and 34. Therefore, the base'current of first transistor 28 is supplied through the resistor 31 fromthe collector of the second transistor 30 and said first transistor 28becomes conductive, and said second transistor 30 becomes nonconductive.If said rotor stops, said first transistor 28 has no current flowingthrough the base, and is nonconductive due to completion of charging ofsaid capacitor 33 or capacitor 34. At the same time, said secondtransistor 30 becomes conductive and has a collector current whichenergizes said solenoid coil 15. When said switch 32 is closed, saidfirst transistor has a base current flowing from the resistor 31 to saidswitch 32, said first transistor 28 is conductive and said secondtransistor 30 is nonconductive, regardless of rotation of the mechanicalswitch.

In the foregoing description, reference designates 30 only a solenoidcoil for actuation of a plunger, but is not restricted to a solenoidcoil for a plunger. In place of the solenoid coil, for example, a coilof a relay, can be used. By using such a relay, coupled with therotation detecting device according to the present invention, otherdevices can be controlled. In addition, a lamp or indicating meter canbe employed in place of the plunger solenoid coil to indicate therotation of the shaft.

In addition to indicating rotation or nonrotation, the rotationdetecting device according to the present invention can be used formeasurement of rotational speed, because the voltage V,,- increases witha decrease in the time of the switching cycle of said mechanical switchand controls the base current of said transistor 14 while said rotationspeed governs the time of said switching cycle. Therefore, it will bereadily understood that a rotation detecting device according to thepresent invention can be used to control the tension of the tape of atape recorder.

We claim:

1. A rotation detecting device comprising a mechanical switch and acontrolling means;

said mechanical switch comprising;

a rotating body including a shaft and a rotor on said shaft, said rotorhaving at least one conductive segment on the surface thereof; and

means for electrically connecting said rotating body with saidcontrolling means including first, second and third contacts positionedto contact the surface of said rotor, the contact point of said firstcontact being spaced equidistantly from the contact points of saidsecond and third contacts, and the contact points of said second andthird contacts being spaced a distance greater than said equidistantspacing, said conductive segment being only slightly longer than thesaid equidistant spacing so that said first contact is electricallyconnected with said second or third contact through said conductivesegment during the rotation of said rotating body, while said secondcontact is never electrically connected with said third contact throughsaid conductive segment, whereby said mechanical switch operates as asingle-pole doublethrow switch; and

said controlling means 3 comprising; a resistor, first and secondcapacitors, apower supply one end of which is grounded, a transistor theemitter of which is grounded, and an actuating coil for a device such asa plunger or a relay which serves as an indicator for said rotationdetecting device, said resistor and first capacitor being connected inseries, the base of saidtransistor being connected to the other end ofsaid power supply through the series connected resistor and firstcapacitor, the collector of said transistor being connected to saidother end of said power supply through said actuating coil, said secondcapacitor being connected between said other end of power supply andsaid first contact, said second contact being connected to the junctionpoint of said first capacitor and said resistor, and said third contactbeing connected to said other end of said power supply, whereby saidmechanical switch is connected to said capacitors so that during therotation of said rotating body said second capacitor is alternatelyconnected in parallel with said first capacitor and in a short circuitwhich forms a discharge path for said second capacitor.

2. A rotation detecting device as claimed in claim 1 wherein said secondand third contacts are diametrically disposed with respect to saidrotor.

3. A rotation detecting device as claimed in claim 1 wherein said rotorhas at least two conductive segments which are spaced equidistantly fromeach other.

4. A rotation detecting device as claimed in claim 1 wherein the valueof the resistance and capacitance of said resistor and. said capacitorshave magnitudes such that sufficient current for energizing saidactuating coil flows into the collector of said transistor when thespeed of rotation of said rotating body exceeds a predetermined speed. I

5. A rotation detecting device as claimed in claim 1 wherein theresistance and capacitance of said resistor and said capacitors are suchthat the collector current of said transistor is continuously controlledaccording to the speed of rotation of said rotating body.

6. A rotation detecting device as claimed in claim 1 further comprisinga current restricting resistor having a low resistance value connectedbetween second capacitor and said first contact so as to prevent thedamage to said contacts and said conductive segment of mechanical switchdue to a surge of current into said second capacitor during the rotationof said rotating body.

7. A rotation detecting device comprising a mechanical switch and acontrolling means:

said mechanical switching comprising;

a rotating body including a shaft and a rotor on said shaft, said rotorhaving at least one conductive segment on the surface thereof; and

means for electrically connecting said rotating body with saidcontrolling means including first, second and third contacts positionedto contact the surface of said rotor, the contact point of said firstcontact being spaced equidistantly from the contact points of saidsecond and third contacts, and the contact points of said second andthird contacts, being spaced a distance greater than said equidistantspacing, said conductive segment being only slightly longer than thesaid equidistant spacing so that said first contact is electricallyconnected with said second or third contact through said conductivesegment during the rotation of said rotating body, while said secondcontact is never electrically connected with said third contact throughsaid conductive segment, whereby said mechanical switch operates as asingle-pole doublethrow switch; and

said controlling means comprising; first, second and third resistors,first and second capacitors, a power supply one end of which isgrounded, a first transistor the emitter of which is directly grounded,a second transistor the emitter of which is grounded through said firstresistor, and an actuating coil for a device such as a plunger or arelay which serves as an indicator for said rotation detecting device,said second resistor and said first and second capacitors beingconnected in series, the base of said first transistor being connectedto the collector of said second transistor through said series connectedsecond resistor and first and second capacitors, the collector of saidfirst transistor being connected directly to the base of said secondtransistor and through said third resistor to the other end of saidpower supply, the collector of said second transistor being connected tosaid other end of power supply through said actuating coil, said firstcontact being connected to the junction point of said first and secondcapacitors, said second contact being connected to the junction point ofsaid second resistor and said first capacitor, said third contact beingconnected to the junction point of the collector of said secondtransistor and said second capacitor, whereby said mechanical switchalternately connects the opposite ends of said series connectedcapacitors t the junction of said capacitors during the rotation of saidrotating body.

8. A rotation detecting device as claimed in claim 7 wherein said secondand third contacts are diametrically disposed with respect to saidrotor.

9. A rotation detecting device as claimed in claim 8 wherein said rotorhas at least two conductive segments which are spaced equidistantly fromeach other.

10. A rotation detecting device as claimed in claim 8 wherein the valueof the resistance and capacitance of said second resistor and saidcapacitors have magnitudessuch that sufficient'current for energizingsaid actuating coil flows into the collector of said second transistorwhen the speed of rotation of said rotating body exceeds a predeterminedspeed.

11. A rotation detecting device as claimed in claim 8 wherein the valuesof the resistanceand capacitance of said second resistor and saidcapacitors are such that the collector current of said second transistoris continuously controlled according to the speed ofrotation'ofsaidrotating body.

12. A rotation detecting device as claimed in claim 8, furthercomprising a current restricting resistor having a low resistance valueconnected between said junction point of said capacitors and said firstcontact so as to prevent the damage to said contacts and said conductivesegment of said mechanical switch due to the discharge current of saidcapacitors during the rotation of said rotating body.

13. A rotation detecting device as claimed in claim 8 wherein saidcontrolling means further includes a switch which is connected acrosssaid series connected capacitors so as to enable said controllingcircuit to be maintained in a given state independent of the state ofsaid mechanical switch.

